Multiple choice

The average marks obtained by a group of 45 students were 16.2. One student left the group as a result of which the average of the remaining students rose to 16.5. But another student came in as a result of which the average marks of the group dropped a bit and became 16.4. What were the average marks obtained by the student who left and the one who joined?

  1. 7.5

  2. 12.5

  3. 15

  4. 16.5

  5. None of these
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A Correct answer
Explanation

Sum of 45 = 45 * 16.2 = 729. One leaves: Sum = 729 - x = 44 * 16.5 = 726. So x = 3. One joins: Sum = 726 + y = 45 * 16.4 = 738. So y = 12. Average of x and y = (3 + 12) / 2 = 7.5.

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